Natural Selection

adaptation

heritable trait or behavior in an organism that aids in its survival and reproduction in its present environment

allele frequency

rate at which a specific allele appears within a population

artificial selection

deliberate manipulation of fitness by humans through selective breeding

directional selection

selection that favors phenotypes at one end of the spectrum of existing variation

diversifying selection

selection that favors two or more distinct phenotypes

evolution

change in allele frequencies of a population across generations

fitness

individual’s ability to survive and reproduce (see also relative fitness)

frequency-dependent selection

selection that favors phenotypes that are either common (positive frequency- dependent selection) or rare (negative frequency- dependent selection)

Peter and Rosemary Grant

study Darwin's finches on the Galapagos Islands and have measured evolution by natural selection over short time scales

good genes hypothesis

theory of sexual selection that argues individuals develop impressive ornaments to show off their efficient metabolism or ability to fight disease

handicap principle

theory of sexual selection that argues only the fittest individuals can afford costly traits

heredity

the transmission of genetic characteristics from parents to offspring

heritability

fraction of population variation that can be attributed to its genetic variance

honest signal

trait that gives a truthful impression of an individual’s fitness

Gregor Mendel

geneticist that first described many characteristics of heredity

natural selection

the non-random and differential reproduction of different genotypes acting to preserve favorable variants and to eliminate less favorable variants

pleiotropy

when a single gene affects multiple traits

polygenic trait

a trait that is controlled by multiple genes

relative fitness

individual’s ability to survive and reproduce relative to the rest of the population

selective pressure

environmental factor that causes one phenotype to be better than another

sexual dimorphism

phenotypic difference between a population's males and females

sexual selection

selection that favors phenotypes that increase ability to obtain or choose good mates

stabilizing selection

selection that favors average phenotypes